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Posted to dev@metamodel.apache.org by kaspersorensen <gi...@git.apache.org> on 2015/10/04 00:11:02 UTC
[GitHub] metamodel pull request: Metamodel 192/datatype conversion function...
GitHub user kaspersorensen opened a pull request:
https://github.com/apache/metamodel/pull/55
Metamodel 192/datatype conversion functions
__Do not merge yet__
This is my first attempt at implementing METAMODEL-192, which thereby is also the first time we make pluggable ScalarFunctions available. I wanted to share it early on since I think some people will find the approach interesting ( @ardlema ?) as inspiration for similar scalar functions (SUBSTRING etc.) ... Please let me know if you think the approach is good or not.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/kaspersorensen/metamodel METAMODEL-192/datatype-conversion-functions
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/metamodel/pull/55.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #55
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commit 94d08404647e53352a07ac37692000aa319a06b4
Author: Kasper Sørensen <i....@gmail.com>
Date: 2015-10-03T20:15:50Z
METAMODEL-192: Updated ScalarFunction interface and added ToXx functions
commit 018a666df5e9dc21e7db9c3ca7f0f041c9986570
Author: Kasper Sørensen <i....@gmail.com>
Date: 2015-10-03T20:27:17Z
Cleaned up the function inheritance patterns, using @Override etc.
commit 3cb4cd8d7c475533f92292baee55e463adca2a57
Author: Kasper Sørensen <i....@gmail.com>
Date: 2015-10-03T22:09:11Z
METAMODEL-192: First impl for client-side eval. JDBC not covered yet.
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[GitHub] metamodel pull request: Metamodel 192/datatype conversion function...
Posted by kaspersorensen <gi...@git.apache.org>.
Github user kaspersorensen commented on the pull request:
https://github.com/apache/metamodel/pull/55#issuecomment-146283048
Reported your idea in METAMODEL-193 - https://issues.apache.org/jira/browse/METAMODEL-193
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[GitHub] metamodel pull request: Metamodel 192/datatype conversion function...
Posted by albertostratio <gi...@git.apache.org>.
Github user albertostratio commented on the pull request:
https://github.com/apache/metamodel/pull/55#issuecomment-146112604
I'd go for the first option. As a first approach I think that is fine to just throwing an exception. I always like to start with the simplest solution and then try to improve it afterwards (if it is needed)
So..my +1 to the first one
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RE: [GitHub] metamodel pull request: Metamodel 192/datatype
conversion function...
Posted by Mario Rasathurai <mr...@infogix.com>.
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-----Original Message-----
From: kaspersorensen [mailto:git@git.apache.org]
Sent: Wednesday, October 07, 2015 9:03 AM
To: dev@metamodel.apache.org
Subject: [GitHub] metamodel pull request: Metamodel 192/datatype conversion function...
Github user kaspersorensen commented on the pull request:
https://github.com/apache/metamodel/pull/55#issuecomment-146204525
Let's create a separate issue in JIRA for that. I could imagine a little parser trick to do it, but I guess for consistency that format is an anomaly compared to other function literals that normally say ```function(argument)``` :-)
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[GitHub] metamodel pull request: Metamodel 192/datatype conversion function...
Posted by kaspersorensen <gi...@git.apache.org>.
Github user kaspersorensen commented on the pull request:
https://github.com/apache/metamodel/pull/55#issuecomment-146204525
Let's create a separate issue in JIRA for that. I could imagine a little parser trick to do it, but I guess for consistency that format is an anomaly compared to other function literals that normally say ```function(argument)``` :-)
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[GitHub] metamodel pull request: Metamodel 192/datatype conversion function...
Posted by kaspersorensen <gi...@git.apache.org>.
Github user kaspersorensen commented on the pull request:
https://github.com/apache/metamodel/pull/55#issuecomment-146143826
OK as far as I am concerned, this story is now complete (assuming Travis builds alright). Could someone give it a code review and then let's merge it if everybody still likes it? :-)
Side-note: I would think we then consider MetaModel 4.4.0 kinda _done_? Anyone else has pending stuff to add before we do a release?
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[GitHub] metamodel pull request: Metamodel 192/datatype conversion function...
Posted by LosD <gi...@git.apache.org>.
Github user LosD commented on the pull request:
https://github.com/apache/metamodel/pull/55#issuecomment-146162602
Looks good to me, but it would be nice to maybe also allow something like SQL's ```CAST <expression> as <type>``` later.
+1
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[GitHub] metamodel pull request: Metamodel 192/datatype conversion function...
Posted by kaspersorensen <gi...@git.apache.org>.
Github user kaspersorensen commented on the pull request:
https://github.com/apache/metamodel/pull/55#issuecomment-146125113
I agree. Would rather finish this quickly, maybe create a JIRA issue for improving it, but have something that works for a limited scope. And I do think that having scalar functions "just" for SELECT clause is already a big deal.
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[GitHub] metamodel pull request: Metamodel 192/datatype conversion function...
Posted by kaspersorensen <gi...@git.apache.org>.
Github user kaspersorensen commented on the pull request:
https://github.com/apache/metamodel/pull/55#issuecomment-146017943
As you can see on my todo-list above, actually now it works in JDBC also and I have improved testing and all.
The only thing that doesn't work (that I know of) is having scalar functions in e.g. the WHERE clause of a JDBC query. I couldn't yet figure out a good way to decompose that problem. I can think of three solution scenarios:
1. Simply not support it, but throw a MetaModel exception when it is attempted. For me this is actually OK to begin with.
1. Have a failover strategy when this happens which uses a QueryPostprocessDataContext and thus eventually one or more full-table-scans to execute the query.
1. Do something really clever to decompose the query and figure out how much of it can be natively executed, do that, and postprocess the rest. This seems very complex so I wouldn't recommend it for now.
What do you guys think? I prefer 1 or 2.
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[GitHub] metamodel pull request: Metamodel 192/datatype conversion function...
Posted by asfgit <gi...@git.apache.org>.
Github user asfgit closed the pull request at:
https://github.com/apache/metamodel/pull/55
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[GitHub] metamodel pull request: Metamodel 192/datatype conversion function...
Posted by kaspersorensen <gi...@git.apache.org>.
Github user kaspersorensen commented on the pull request:
https://github.com/apache/metamodel/pull/55#issuecomment-145617761
Great, then I'll continue down this line ...
A few TODOs that I can think of:
- [ ] More rigoruous testing - does it also work in filter items, does it work in subqueries and all that.
- [ ] Add some hooks to the query parser to understand it.
- [ ] Maybe also add aliases in the query parser? I notice that for scalar functions there are often different names for the same thing in many SQL dialects.
- [ ] Add JDBC support by querying the IQueryRewriter interface whether or not particular scalar functions are supported.
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[GitHub] metamodel pull request: Metamodel 192/datatype conversion function...
Posted by albertostratio <gi...@git.apache.org>.
Github user albertostratio commented on the pull request:
https://github.com/apache/metamodel/pull/55#issuecomment-145520371
Really nice approach!
I woudl add some unit tests for TO_STRING, TO_DATE and TO_BOOLEAN functions.
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